1. Field of the Invention
The present invention relates to a barrier net across a space defined by the fuselage of an aircraft, for example for restraining the movement of cargo in the fuselage of an aircraft.
2. Description of Related Art
Barrier nets formed from webbing or rope type textile elements are commonly used to act as emergency restraints for the payload on freighter aircraft in the event of an emergency landing. Typically, they have to restrain a forward loading based on the payload mass multiplied by a 9 g forward acting inertial factor. This generates extremely large forces within the barrier net, which, in turn, are transmitted into the aircraft structure to which the barrier net attaches.
It is in the nature of textiles, that loads can only be transmitted by way of tensile forces along the elements, because these have no strength in shear or compression. In order for an element to react to a loading imposed at right angles to it, as the initial loading on a barrier net would be, it must deflect in the direction of the applied load such that, at equilibrium, the summation of the forward load components of the tension loads in the net at each attachment equals the applied load. Clearly, the more a net deflects, the closer the elements at the attachments will rotate to approach the direction of the applied load and the lower the tension in those elements would have to be for a given forward load component; the tension being equivalent to the load vector tangential to the net member at the attachment. This would translate into a design philosophy to allow for as much deflection as possible in order to keep the internal tensions in the net as low as possible, thus requiring lower strength elements, which would generally mean that less material need be used, leading to a lighter and cheaper product.
However, operational and space constraints on the aircraft normally dictate that barrier net deflections must be kept as small as possible, thus conflicting with the above philosophy. Unfortunately, restricting the deflection of the barrier net not only implies a heavier net, or the use of more sophisticated ‘low elongation’ materials, but it also increases the radial components of the tension loads at the attachments, which then take on an increasing significance. In addition to restricting the allowable net deflection, the aircraft manufacturer may also impose a radial load limit on the attachments. Often, it is extremely difficult to balance these conflicting requirements in the net design.
It is an object of the present invention to go at least some way towards overcoming the disadvantages of the prior art devices, or at least to provide an acceptable alternative to the prior art devices.